The invention relates to a non-diluting particle study device and more specifically to a device for ejecting a non-diluted specific minute amount of fluid sample containing particles into a flow stream leading to a sensing zone in the particle study device.
Heretofore, in the field of particle analysis and particle study, such as the study of red and white blood cells in a blood sample, it has been common practice to dilute the blood sample and then to pass a portion of the diluted sample through a sensing zone in a particle study device. The blood is diluted because the normal human blood count is five million cells per cubic millimeter and it is only necessary to study or analyze one hundredth of that amount, namely, a volume of 0.01 cubic millimeters.
In studying a blood sample, the blood cells in a given amount of the sample are counted by passing a portion of the diluted blood sample through a sensing zone in a particle analyzing device, such as a Coulter type particle analyzing device which operates on the Coulter sensing principle disclosed in U.S. Pat. No. 2,656,508 issued Oct. 20, 1953 to Wallace H. Coulter.
According to this principle, when a microscopic particle in suspension in a fluid electrolyte is passed through an electrical field of small dimensions approaching those of the particle, there will be a momentary change in the electric impedance of the electrolyte in the ambit of the field. This change of impedance diverts some of the excitation energy into associated electrical circuitry, giving rise to an electrical signal. Such signal has been accepted as a reasonably accurate indication of the particle volume for most biological and industrial purposes.
One apparatus of the Coulter type includes first and second vessels each containing a body of fluid electrolyte. The second vessel is smaller and is immersed in the electrolyte in the first vessel. An electrode extends into the electrolyte in each vessel and electric current flows between the electrode through an opening in the side wall of the second vessel, the opening consisting of a minute aperture commonly referred to as a Coulter aperture. Flow of liquid between the vessels is caused by applying vacuum to the second vessel. According to the Coulter principle, particles passing through the aperture from one body of electrolyte to the other body of electrolyte will change the impedance of the electrolyte contained within the aperture and this change in impedance is sensed by the electrodes. This change generates an electrical signal in the form of a particle pulse which is then counted by the electrical circuitry of the particle analyzing device.
When making a blood analysis a dilution of blood in electrolyte is placed in the first vessel. Then vacuum is applied to the second vessel to cause diluted blood to flow from the first vessel through the aperture into the second vessel for a specific period of time. The second vessel is filled with electrolyte, probably including prior dilutions.
To make a fairly accurate measurement of particle concentration, one must accurately measure or meter the amount of fluid which passes through the sensing zone during a period of time when the electrical circuitry of the device is operative. This can be accomplished by passing fluid through the sensing zone at a given flow rate for a specified period of time. Apparatus utilizing fluid flow metering systems of this type in a fluid analyzing device are disclosed in U.S. Pat. Nos. 3,577,162 and 3,654,439.
In most Coulter type particle analyzing devices, the metering is accomplished with a fluid metering apparatus of the type disclosed in U.S. Pat. Nos. 2,869,078, 3,015,775 and 3,271,672. Such metering apparatus includes a closed fluid system hydraulically connected to the second vessel. The closed fluid system includes a connection to a vacuum source and a mercury manometer. When operating the device, vacuum is applied to the closed fluid system to raise the mercury in the manometer and to draw some fluid sample into the second vessel. The connection to the vacuum source is then closed and the manometer, by reason of the mercury flowing downwardly to its original position, causes liquid to be drawn through the aperture and generates signals indicating the beginning and the end of an analytic run in a period during which an accurately metered volume of fluid is passed through the aperture. The metered volume of fluid is equal to the volume within the manometer between two electrodes.
It will be understood from the foregoing description of a Coulter type particle analyzing device that it is necessary to dilute a quantity of blood, to make an accurate determination of dilution and to accurately meter the fluid flow through the Coulter aperture in order that an accurate count of blood cells can be made. A simpler way of making the particle analysis or study would be to pass a specific minute amount of undiluted blood through the Coulter aperture and thereby eliminate the manometer and diluter systems. A device for ejecting a specific minute amount of particle-containing fluid such as blood into the flow stream leading to a sensing zone in a particle analyzing device is shown in the Parent Patent Application Ser. No. 473,127 filed May 24, 1974 and U.S. Pat. No. 3,859,012.
In both the above noted patent application and patent, circuitry is disclosed for operating the ejecting device. The circuitry provides a predetermined amount of electrical energy to the device causing it to increase in temperature, expand and eject a specific amount of fluid. The amount of energy provided is determined mathematically and, in the embodiment described therein, is the amount of energy necessary to raise the temperature of the device twenty degrees, a twenty degree rise causing a specific expansion and therefore an ejection of a specific amount of fluid.
If sufficient thermal insulation is used to ensure that heat loss during a heating cycle is negligible so that all the energy supplied is stored as heat in the expansive element an extended cool-off period is desirable. Extended cool-off periods are undesirable from an operational point of view. On the other hand, if the insulation is designed to permit rapid cool-off, the heat loss during the expansion period must be taken account of and compensated for. This is unsatisfactory because neither the temperature gradient across the insulation nor the ambient temperature are fixed and/or well known quantities. Consequently, it would be preferable to measure temperature rise within the ejecting device rather than the specific amount of supplied energy.